The present invention is directed to a process for making a meterable and flowable form of cellulose, and the product made therefrom. The product is a flake and is used in cementitious compositions that require cellulose fibers to be mixed therein.
One of the many uses of cellulose fibers is as a reinforcing material in cementitious products, such as those containing concrete, chalk, asphalt, bitumen, plaster, cement, gypsum, mortar, and the like. Cellulose fibers for use in these materials are typically supplied from commercially available market pulp sheets. Some pulp sheets are rolls of lightly pressed fluff pulp sheets. Other market pulp is papergrade, which is a more tightly pressed sheet. In order for cellulose fibers from a pulp sheet to be more fully assimilated within the cementitious product, the sheets must first be broken up with the use of a mechanical device, typically a hammermill, that fiberizes the sheet into singulated pulp fibers. The pulp fibers are then added to the product. Sometimes the market pulp sheet is diced and the diced pulp sheet is added. Papergrade pulp sheet being more densified than fluff pulp sheet, consequently is more difficult to disperse (has longer dispersion time) in wet media than fluff pulp sheet. In attempts to improve the dispersibility, either type of pulp sheet can be hammermilled or diced. However, once singulated into individual fibers, the fibers are considered to be undesirable because of their inability to be metered. Some pulp sheets, especially of the fluff type, are more readily dispersible. Sheets, however, are incapable of flowing in conduits and are too large to be metered in precise quantities for cementitious products. Dicing pulp sheet is also undesirable, since dicing, like hammernilling, requires additional processing prior to dispersing the fibers. Dicing also leads to localized highly densified areas or xe2x80x9cedge effectsxe2x80x9d at the shear points that reduces the capacity of those densified areas of the fibers to disperse. The disadvantages of pulp sheet makes finding a new form of cellulose having none of the aforementioned drawbacks more urgent. U.S. Pat. Nos. 5,407,139 and 6,345,777 describe mechanically refiberizing cellulose products prior to their application in asphalt and cement. Refiberizing the cellulose materials immediately prior to application adds unwanted complexity and cost to the structures built from these materials. U.S. Pat. No. 5,931,610 describes a method for mechanically breaking up clumps of synthetic fibers. German publication Offenlegungschrift DE 100 09152A1 describes making dense cellulose and synthetic fiber pellets.
It would be advantageous to provide a fibrous cellulose product that does not require mechanical fiberizing of the fiber source once dried. Ideally, such product would be easier to meter much better than singulated fibers. It is also desirable that the new fibrous product have a wet dispersability comparable to the presently available pulp sheets, but that avoids the need for hammermilling. The present invention fulfills these needs and provides further related advantages.
One embodiment of the present invention is directed to a new form of pulp: a flake having a specific size, density, and wet dispersibility. The flakes are easy to meter in specified quantities when adding to cementitious products, because bulk quantities of the flakes flow well in conduits and other enclosed containers. The pulp flakes can supply cellulose fiber sufficient to an extrusion or high consistency mixing process due to the flake""s high density relative to hammermilled pulp. The pulp flakes have a wet dispersability that is comparable to some pulp sheets that have not been hammermilled.
In one embodiment of the invention, a pulp flake is provided that has a wet dispersion of from about 60 to about 240 counts as measured by a standard British disintegrator. Another embodiment of a pulp flake has a density of about 0.3 to about 0.7 g/cc. In one embodiment of the invention, an adjuvant is added to the pulp flake. The adjuvant can be a coupling agent, silicate, zeolite, latex, crosslinker, dye, debonder, surfactant, dispersant, clay, carbonate, biocide, antimicrobial, flame retardant, preservative, synthetic fiber, glass fiber, carbon fiber, or any other natural fiber. In one embodiment, the pulp flake has a wet dispersion measure of about 60 to about 90 counts when treated with a debonder. The pulp flake has a size of about 3-5 mm3. The density of the pulp flake is about 0.3 g/cc, but can be as high as about 0.7 g/cc.
In another embodiment of the invention, a process for making singulated pulp flakes is provided. The process includes dewatering liquid pulp stock to a consistency of about 30 to about 50% solids. The process includes initial flaking to break up the dewatered pulp bundles into semi-uniform flakes having a median size of from about 3 to about 5 mm3 and a consistency of from about 33 to about 55% solids. The process includes drying the flaked pulp to a consistency of from about 85 to about 97% solids. The process includes flaking a second time to separate the flakes that may have bonded during drying. The product xe2x80x9csingulatedxe2x80x9d flakes then go to a baler for packaging. In another embodiment, the process includes blending the liquid pulp stock with at least one adjuvant prior to dewatering.
In another embodiment, a cementitious product is provided. The cementitious product includes cellulose fibers from pulp flakes. The pulp flakes have a dispersion measure of 60-240 counts prior to addition to a precursor composition that forms the cementitious product.
Pulp flakes made according to the invention do not require refiberizing prior to their addition to cementitious products due to their high dispersibility. Pulp flakes made according to the invention can be metered more readily than hammermilled fluff pulp because of their size and density. The pulp flakes of the present invention can be dispersed more readily than most diced pulp sheets because of their lower density and lack of cut edges.